DIY Arrow Spine Tester
My Version of the DIY Arrow Spine Tester. The images should be self explanatory.
Arrow spine is a measure of stiffness which is gauged by how much the arrow flexes when weight is applied. The spine, or “stiffness”, of an arrow is a simple concept to understand, yet its importance is often overlooked.
Arrow spine is a critical component of archery accuracy. Here is my version of a simple spine tester.
You use the spine tester to:
Sort Arrows for similar spine
Align your knock so they follow the “backbone” or typically the grain pattern
When you place the arrow in the tester, start with the grain going horizontal (see why in the image below)
The Archery Trade Association standard for measuring arrow spine requires this test: Suspend a 1.94-pound weight at the shaft’s center, and use a machine to measure the deflection or bend at that point. Deflection is measured in inches. Some typical deflection measurements are .500, .400 and .350. These measurements correspond to the spine sizes most manufacturers use to mark arrows.
For wood arrows the distance between the supports should be 26″
If i have a specific spine I want when making my arrows i start with a shaft size slight larger, then plane down to get within a 5 pound shaft. It seems to be a recommendation to stay within a 5 pound variance.
Why do you need a DIY Arrow Spine Tester
MIKE MEUSEL explains it well; When an arrow is shot out of a bow, compound or traditional, it undergoes what is called archer’s paradox. There are various definitions for it, but it describes the effect of an arrow bending upon being shot. The arrow bends around the riser, and continues to flex back and forth on its way to the target. There are some great slow motion videos on the internet that catch the paradox of the arrow in flight. What seems fairly inflexible in the hand becomes a piece of wet spaghetti when shot out of a bow. Because the arrow is being pushed from behind, it bends as the nock end of the arrow accelerates faster than the point end of the arrow. How much the shaft bends affects the impact point of the arrow left and right. This is where the spine of the arrow comes in.
Note on the amo chart below i add the measurements as I get them so I don’t have to calculate them each time.
The Next image shows the direction of the nock